Serendipitous discovery of a brightening quasar at redshift z = 3.68

We report the serendipitous discovery of a redshift 3.68 quasar while validating the star WD 0308‐565 as a spectrophotometric standard star for the Multi‐Unit Spectroscopic Explorer (MUSE) calibration plan. Based on the MUSE observations, the luminosity of the quasar at 1350A (L1350) is 4.71 × 1045 erg s−1. The black hole mass is 2.5 × 109 Mʘ, and bolometric luminosity is 1.57 × 1047 erg s−1. Present in the field of view of a star in the calibration plan of the instrument makes this a very valuable quasar as it will receive many repeated visits in the coming years making it an ideal candidate for reverberation mapping studies.